Investigation of Detector/Source instability in the Inel diffractometer
Krishna Nittala, May 21, 2009
It is desirable to know if there is any drift in the X-ray source or the CPS detector
in the Inel Diffractometer. For this purpose, acquisitions were taken over a 1 hour period
and the fluctuations in the intensities of the diffracted peaks were plotted. Silicon
powder was used as a standard for this procedure. Each acquisition was taken for a
total time of 30 s. Peak fitting of the diffraction patterns was done in MATLAB using a
modified Pearson VII function to include contributions from both Kα1 and Kα2. Figure
1(a) shows the typical XRD pattern obtained for Silicon in the Inel Diffractometer. The
integrated intensities of different peaks obtained from peak fitting procedure were used
to check for detector/source instability. The plot of the errors ( Iobs-Imean) for peaks at
different 2 positions are plotted as a waterfall plot and are shown in Figure 1(b). The
confidence intervals shown are the 95% upper and lower bound intervals generated by
the MATLAB curve fitting routine.
(a)
(b)
Figure 1: (a) Typical XRD pattern for Si powder in the Inel Diffractometer and (b) error
plots for peaks observed at different angles showing the fluctuation of the peak intensity
with time. No trend is observed for any of the peaks
It is possible that there might be (1) source fluctuation and/or (2) detector
instability. Source fluctuation will be represented in all of the peaks at the same time.
However, no correlation has been found between the errors in Figure 1(b). On the other
hand, detector instability would be different at different 2 positions. The variation of the
peak integrated intensity would not be correlated for peaks at different 2 positions.
From the error plot shown in Figure 1(b), there is a slight drift in the integrated peak
intensity for 2 = 47 o while no drift is observed for any of the other peaks. Linear fit of
the errors at this 2 position resulted in a slope of m = 0.03 while the same for the rest
of the peaks was m ~ .003 or lower. However, the drift is not very significant at least in
the time for which the experiment was conducted.
Hence, there is no source or detector instability in the Inel Diffractometer for T<1 hr.